'A number of' is treated as plural, so the correct verb form is 'are'.

The subject 'pair' is singular, so the correct verb form is 'is'.

'Data' is a plural noun, so it should be 'The data were collected'.

The phrase 'each of' requires a singular verb, which is 'has'.

When using 'either/or', the verb agrees with the nearest subject, which is 'dogs' (plural), so 'are' is correct.

The subject 'pair' is singular, so the correct verb form is 'is'.